Not true. People may have the gene that allows them digest lactose as children, but if you lock a man without the mutation that in a room with nothing but milk, he'll never be able to digest it no matter how long you leave him there, no matter how great the need. A mutation has to occur.
No, he can't, but what if this happens with his grandchildren:
http://encarta.msn.com/media_461547549_761564762_-1_1/Recessive_Gene_Transmission.html
Absolutely true, I gave you a specific example. And a mutation is a change. What do you think turning something on or off is? It is a change. Here is the composition of HUMAN breast milk.
Major nutrients. Lactose, 5.5-6.0g/dL, is the most constant nutrient in human milk (Table I). Its concentration in breast milk is not affected by maternal nutrition. Proteins amount to about 0.9g/dL in mature milk.[12]Recent studies comparing the impact of nutrition on lactation in industrialized and developing countries suggest that neither maternal diet nor body composition affects milk protein level.[1] However, limited data from earlier studies seem to indicate that short-term, high-protein diets can increase the protein and nonprotein nitrogen content of human milk,[13] while limiting maternal food intake can lead to lower milk protein levels.[13-15]